Get rid of inefficient uses of childNodeCount()

Source/core/dom/ContainerNode.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 519 matching lines @@
         // Removing a node from a selection can cause widget updates.
         document().nodeChildrenWillBeRemoved(this);
     }
 
 
     NodeVector removedChildren;
     {
         RenderWidget::UpdateSuspendScope suspendWidgetHierarchyUpdates;
         {
             NoEventDispatchAssertion assertNoEventDispatch;
-            removedChildren.reserveInitialCapacity(childNodeCount());

[Inactive, 2014/02/19 04:13:33]

I don't think this one is worth it as we end up traversing the children twice
instead of once for a likely small win on Vector::append().

[eseidel, 2014/02/19 05:39:54]

I expect walking the child list twice may be cheaper than a possible extra
malloc.  But I could be wrong.  I would expect this change to be visible on
microbenchmarks (one way or the other).  This function has historically ben
quite hot.

[Inactive, 2014/02/19 14:28:15]

Ok then. I prefer to keep this change out of the CL. We can try this one out
separately if we want to.

             while (m_firstChild) {
                 removedChildren.append(m_firstChild);
                 removeBetween(0, m_firstChild->nextSibling(), *m_firstChild);
             }
         }
 
         childrenChanged(false, 0, 0, -static_cast<int>(removedChildren.size()));
 
         for (size_t i = 0; i < removedChildren.size(); ++i)
             ChildNodeRemovalNotifier(*this).notify(*removedChildren[i]);
@@ skipping 487 matching lines @@
         return true;
 
     if (node->isElementNode() && toElement(node)->shadow())
         return true;
 
     return false;
 }
 #endif
 
 } // namespace WebCore